Our studies will analyze the thymic peptides FTS (serum thymic factor), thymosin alpha-1 and thymopoietin which induce in vitro differentiation of prothymocytes into T lymphocytes. Synthetic peptides, fragments and analogs of these peptides will be synthesized, and peptide-protein or peptide-linker conjugates will be prepared and used as immunogens for the production of rabbit antibodies and mouse monoclonal antibodies specific for FTS, thymosin alpha-1 and thymopoietin. Radioimmunoassays (RIAs) for the thymic peptides will be developed, using rabbit or monoclonal antibodies and synthetic peptides as the hormone standards and radioiodinated tyrosine analogs as the tracers. These assays will be used to identify the specific antigenic sites recognized by these antibodies and to detect the presence of thymic hormones in human peripheral blood, thymic and peripheral lymphoid tissues and skin. RIAs will also be used for the quantitation of FTS, thymosin alpha-1 and thymopoietin in human plasma in health and diseases. Analysis of receptors for thymic hormones on certain lymphoid cell populations will be undertaken, using fluorescent and radiolabeled derivatives of the thymic peptides. These studies will advance our knowledge of the role of thymic hormones in the normal state and in a variety of immunodeficiency diseases and cancer. We have developed four RIAs for the quantitation of FTS. To establish these assays, we synthesized pure FTS, used as the hormone standard, and two tyrosine FTS analogs. The latter showed full FTS immunoreactivity, and their radioiodinated derivatives are used as tracers. Two assays used the antiserum from a rabbit immunized with an FTS-protein conjugate and the others used a mouse monoclonal antibody against FTS. One of these RIAs is being optimized to allow quantitation of FTS levels in human plasma. The detailed antigenic specificity of the anti-FTS antibodies was determined by measuring the ability of FTS and 12 synthetic FTS peptide analogs to compete with a radioiodinated FTS analog in these RIAs. The mouse monoclonal antibody and the rabbit antiserum showed similar structural requirements for binding of the FTS peptides. Both antibodies were relatively specific for molecules ending in --Xxx-Xxx-Gly-Gly-Ser-Asn-OH, which corresponds to the biologically active region of FTS.